(1) Field of the Invention
The present invention relates to joined bodies in which members are joined together through an intermediate member. More particularly, the invention relates to joined bodies of such a structure as suitable for joining members having different coefficients of thermal expansion, for instance, a ceramic member and a metallic member.
The present invention also relates to a method of joining members having different coefficients of thermal expansion.
(2) Related Art Statement
In order to join members having different coefficients of thermal expansion through butting and bonding, a technique has been known to join these members while an intermediate member is interposed at an interface therebetween. For instance, Japanese utility model registration application Laid-open No. 59-160,533 discloses, as a joining structure between a ceramic member and a metallic member, a method of joining them with a clad made of a tungsten material or an Mo material is interposed at an interface therebetween.
However, according to the above mentioned methods, sufficient joining strength cannot be obtained because residual stress is produced at the joining interface due to difference in thermal expansion between them. Now, explanation will be explained with reference to joining between a metallic member and a ceramic member as shown in FIG. 4. Assume that the metallic member is joined to the ceramic member in a desired shape before cooling. Once the metallic member and the ceramic member having larger and smaller coefficients of thermal expansion, respectively, are cooled, the metallic member shrinks more than the ceramic member. Consequently, as shown in FIG. 4, tensile stress is exerted upon each of the metallic member and the ceramic member at an edge A of the interface. When this state proceeds, the members peel or crack at the interface edge A.
When a clad made of a tungsten or molybdenum material is used as an intermediate layer, residual stress is removed to some extent as compared with the above-mentioned case where both the members are directly joined together. However, since this intermediate layer is not provided to remove the residual stress at the joining interface, it was not possible to prevent peeling or cracking at the joining interface.